Sound-transducing apparatus



United States Patent Ofi 3,013,127 Patented Dec. 12, 1961 ice 3,013,127 SOUND-TRANSDUCIN G APPARATUS Raymond T. Christensen, Itasca, and Leonard E. Wo cik,

Franklin Park, IlL, assignors to Zenith Radio Corporation, a corporation of Delaware Filed May 27, 1959, Ser. No. 816,186 12 Claims. (Cl. 179-114) This invention relates in general to sound-transducing apparatus for converting sound into electrical signals, or vice versa. More particularly, it pertains to an arrangement utilized in conjunction with a sound-transducing device for optimizing or controlling the frequency response characteristic of that device.

A sound-transducing device, such as a transmitter, microphone, receiver, earphone, or the like, exhibits a certain natural resonance frequency due to its mechanical and acoustical elements. If the transducer is relatively large, with respect to physical size, the resonance frequency is usually at such a low point in the spectrum that no adverse effects are encountered. On the other hand, for relatively small sound transducers the resonance frequency occupies a higher position in the frequency spectrum and must be taken into account in designing the device in order that an undesirable response peak, resulting in distortion, is not manifest in the audible range.

One convention-a1 way of attenuating or cutting down a resonance peak in the response characteristic of a sound transducer is to incorporate damping fabric or cloth into the device. This expedient, however, suffers from the disadvantage that the relatively high frequency components are also attenuated at the same time. Moreover, if the undesirable peak is too extreme it is not possible to attenuate it to the extent required to achieve a uniform response. Another well known approach for compensating the elfect of the resonance frequency of a sound-transducing device resides in providing a relatively long sound inlet or outlet, depending on whether the device takes the form of or is used as a microphone or receiver, to the diaphragm. The particular cross-sectional area and length of the sound path or channel determine the amount of compensation introduced.

While it constitutes only a minor design problem to provide a restricted sound path to or from the diaphragm for most sound transducer-s, when the device must be miniaturized so that it occupies a very small physical volume, as is the case with some of the sound-transducing devices used, for example, in hearing aids that are incorporated in eyeglass spectacle frames or other onthe-head type hearing aids, the problem assumes major proportions if the sound channel is to be included without appreciably increasing the size of the device. To this end, the present invention is directed to a novel construction of a sound-transducing device that meets the problem without actually increasing the physical size of the device to any considerable degree. Furthermore, the cost of the device is not increased to any substantial degree.

Accordingly, it is an object of the present invention to provide a new and improved sound-transducing apparatus.

It is another object to provide a sound-transducing apparatus that exhibits a particular frequency response.

A sound-transduoing apparatus, constructed in accordance with the invention, comprises a sound-transducing device which includes an electro-mechanical converting assembly to which is connected a diaphragm. A first cover plate is mounted on the sound-transducing device covering, but spaced apart from, the diaphragm on the side opposite from the electro-mechanical converting assembly to form a chamber between the first cover plate and diaphragm. A second cover plate covers the first plate. The two plates are formed to provide a channel therebetween with each of the cover plates having at least one aperture therein opening into the channel to provide a sound path connecting with the chamber and extending through both of the plates and through at least a portion of the channel.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to the following description in conjunction with the accompanying drawing, in the several figures of whichlike reference numerals indicate identical elements, and in which:

FIGURE 1 is a plan view, partially cut away, of a sound-transducing apparatus constructed in accordance with one embodiment of the invention;

FIGURE 2 is a sectional view of the sound-t'ransduoing apparatus of FIGURE 1 taken along the lines 22;

FIGURE 3 is another sectional view of the soundtransducing apparatus taken along the lines 3'3 of FIG- URE 1;

FIGURE 4 is an end view, also partially cut away, of the sound-transducing apparatus of FIGURE 1;

FIGURE 5 is a plan view of another sound-transducing apparatus, also partially cut away, constructed in accordance with another embodiment of the invention; and

FIGURE 6 illustrates a family of frequency response characteristics utilized in describing the operation of both of the illustrated sound-transducin-g apparatus.

Referring to the apparatus shown in FIGURES 1-4, a generally flat, rectangular shaped diaphragm 10 is rigidly connected by means of a drive pin 12 to an electromechanical converting assembly in the form of a magnetic motor assembly. The connection between the diaphragm and the pin is provided by a quantity of cement or wax 13. Of course, any one of a variety ofdiiferent sound-transducing devices may be employed, such as that characterized as a capacitance transducer, a dynamic transducer, a piezo-electric transducer, or the like. As far as the present invention is concerned, the specifications of the elements below diaphragm 10, as illustrated in FIGURES 2 and 3, are of no particular concern.

The magnetic motor assembly shown is of the conventional balanced magnetic bridge type wherein drive pin 12 is connected to an armature reed 15 constructed of order that the drive pin may clamp around armature reed 15 to provide a substantially rigid connection thereto. Reed 15 itself is mounted on only one end thereof in cantilever fashion. Specifically, 'the mounted end of reed 15 is sandwiched between a pair of substantially identical O-shaped pole pieces 17, 18 and also a pair of nonmagnetic, such as brass, spacers 19. Spacers 19 separate reed 15 from pole pieces 17 and 18. The pole pieces are threaded and appropriate holes are provided in spacers 19 and reed 15 in order that the entire pile up may be assembled and held together at that point by means of a screw 21. This screw additionally mechanically connects the assembly to a nonmagnetic-base mounting plate 23'through a non-magnetic spacer 24.

As is the case with a balanced magnetic bridge type transducer, pole pieces 17 and 18 are shaped so that they are adjacent, but spaced apart from, both sides of the free or vibrating end of reed 15. A single non-magnetic spacer 25, also preferably made of brass and having a and reed 15, is positioned between pole pieces 17 and 18 3 next to the free end of reed 15. A screw 27 is threaded into pole pieces 17 and 18 at that point and extends through holes in spacers 24 and 25 in order to hold these units together and also to provide an additional mechanical connection to base plate 23.

A pair of bar magnets 28, 29 of rectangular cross section are mounted between pole pieces 17 and 18 on opposite sides of, and parallel to, reed 15. Screws 21 and 27 also serve to hold the bar magnets in place. This arrangement is best seen in FIGURE 3. Magnets 28 and 29 may be magnetized with the polarity shown, namely with the north poles nearest diaphragm while the south poles are farthest from the diaphragm. Accordingly, pole piece 17 is of north polarity and pole piece 18 is of south polarity.

A coil form 31 is positioned within the central portion of the arrangement of pole pieces 17 and 18 and bar magnets 28 and 29 and an opening of rectangular cross section is provided in its center to permit reed to pass therethrough. In this way, the coil form surrounds reed 15 and yet there is sufiicient clearance to enable the reed to vibrate without touching the form. A coil 32 is wound around coil form 31.

The extreme periphery of base plate 23 is aflixed, for example by means of a suitable cement, to the open side of a five-sided housing 34 so that the sound transducer may be encompassed on all sides other than that to which diaphragm 10 is connected. Wire conductors 35 provide electrical connections from the two terminals of coil 32 to a pair of terminals 36 on housing 34. Preferably wires 35 are soldered to the terminals.

A cylindrically shaped tube 38, commonly called the Thuras tube, has one end rigidly mounted to an aperture of housing 34 and the other end extending into the space within the housing beneath diaphragm 10 to provide a sound path from that space to the atmosphere external to the sound transducer.

As thus far described, the arrangement of elements is entirely conventional. Such a construction, however, particularly when the elements have been miniaturized or scaled down to provide sound transducer action in a relatively small space, may exhibit a frequency response characteristic that is undesirable. Response curve 40 in FIG- URE 6 is typical of that which is likely to result from the arrangement thus far described when the elements are scaled down. It will be noted that there is an extremely high undesirable peak lying in the vicinity of 2500 cycles per second. By employing conventional damping techniques, such as utilizing damping fabrics, the undesirable peak of response 40 may be reduced somewhat but not to the extent required to provide a relatively flat response without causing the high frequency components to be attenuated unnecessarily. Curve 40 varies too widely to permit appropriate compensation. In accordance with the present invention, the response characteristic is made much more uniform than that of curve 40 by providing a sound inlet to, or outlet from, diaphragm 10, depending on whether the described transducer is employed as a microphone or a receiver.

Specifically, a first rectangular shaped cover plate 42, having overall dimensions slightly larger than diaphragm 10 and having a series of three 90 parallel bends around its entire periphery, is mounted over, but spaced apart from, diaphragm 10, being crimped around or cemented to the peripheral edge of mounting plate 23 and a portion of housing 34. By establishing a spaced-apart relation between diaphragm 10 and cover plate 42, a chamber 43 is formed therebetween. An aperture 44 is provided in the central portion of cover plate 42 in order to permit the waxing of drive pin 12 to diaphragm 10 in the manufacture or assembling of the apparatus. The three right angle bends at the periphery of cover plate 42 provide a stair shaped configuration such that an olfset 45 results.

A second rectangular shaped cover plate 47, which is slightly larger than plate 42 and has a single 90 bend at its periphery, is mounted over cover plate 42 and is crimped or cemented to the extreme periphery of plate 42. Second cover plate 47 is continuous in its central region and thus aperture 44 is completely covered or sealed; as indicated in the drawings, cover plate 47 is disposed over the electro-mechanical converting assembly and has a shape which defines with the latter a cavity which is separated into two chambers by diaphragm 10. Of course, in constructing the assembly, drive pin 12 is connected to diaphragm 10 before cover plate 47 is afiixed. Since cover plate 47 has only a single bend around its periphery, a channel 50 of substantially square cross section results between first and second plates 42, 47 and extends around or loops the entire periphery of diaphragm 10. Channel 50 thus has four legstwo short and two long.

Cover plate 47 has an aperture 52 adjacent channel 50 and cover plate 42 has an aperture 53 also adjacent channel 50 (best seen in FIGURE 1) in order to provide a sound path to or from chamber 43 and the outside atmosphere. Apertures 52 and 53 are substantially diametrically positioned, each located in one of the long legs of the channel, and thus there are actually two sound paths to or from chamber 43 of substantially equal length; namely, each path is approximately /2 the total length of channel 50, which of course is approximately the perimeter of diaphragm 10.

In the operation of the sound-transducing apparatus of FIGURES 1-4, and assuming that the apparatus is utilized as a microphone, sound waves reach chamber 43 by way of apertures 52 and 53 via channel 50 as shown by the arrows associated therewith with FIGURES 1 and 3 and impinge upon diaphragm 10 which causes excitation thereof in well known manner. When diaphragm 10 is at rest, the magnetic bridge is in balance and substantially all of the magnetic lines of flux extend between pole pieces 17 and 18 with no appreciable flux flowing through reed 15. However, when diaphragm 10 vibrates back and forth responsive to the impingement of sound waves, such vibrations are transferred to reed 15 causing the free end of reed 15 to likewise vibrate in the space between the two pole pieces. This unbalances the bridge in conventional fashion, resulting in the flow of a varying amount of flux through reed 15 to in turn induce an electrical signal in coil 32 which may be picked off or derived at terminals 36.

It has been found that the unique sound communicating channel 50 provided by the arrangement of FIG- URES 1-4 results in a frequency response characteristic as shown by curve 55 in FIGURE 6. While it is true that there are two peaks in response curve 55', they are of a magnitude very small compared to that of the un desirable peak of response 40, and thus may be flattened down or attenuated by the use of filter or damping cloth (not shown), with the result that a substantially more uniform response characteristic is obtainable than that which may be achieved in the absence of the invention. Since considerably less damping is required to flatten the peaks in curve 55 as compared to that required to attenuate the single peak in curve 40, there is a corresponding reduction in the effect on high frequencies.

In a sound-transducing apparatusconstructed according to FIGURES 14, and operated very satisfactorily, channel 50 had cross-sectional dimensions of approximately .035 x .035 inch and each of the two sound paths had a length of approximately .83 inch.

The particular positions and relative amplitudes of the peaks in the response characteristic may be altered by changing the cross sectional area of channel 50 or by varying the positions of apertures 52 and 53 with respect to each other. In general, by increasing the length of the sound path or decreasing the cross-sectional area of the channel, the resonant energy is effectively moved toward the lower frequency portion of the frequency spectrum.

The dimensions of holes 52 and 53 are not critical so long as they are not pin size.

Control also may be exercised by employing more than one aperture in plate 42. To illustrate, in the FIGURE embodiment there are two apertures 57, 58 in first cover plate 42 which connect channel 50 to chamber 43 between diaphragm and cover plate 42. Apertures 57 and 58 may be spaced at any desirable points along channel '50 in order to achieve optimum performance. As shown, each is located in one of the short legs in channel 50 such that the sound traveling to the chamber is translated through two sound paths of difierent lengths.

With apertures 57 and 58 located substantially as shown in FIGURE 5, a response characteristic as represented by curve 60 in FIGURE 6 has been obtained. As in the case of curve 55, response 60 also has two peaks but they may likewise be flattened out by filter cloth to achieve a somewhat more uniform frequency response. A sound-transducing apparatus has been constructed in accordance with the teachings of FIGURE 5 and operated very satisfactorily. The cross-sectional dimensions of channel 50 were approximately .035 x .035 inch. The length of the sound path from aperture 52 to aperture 58 was .41 inch and the length of the sound path between apertures 52 and 57 was .53 inch.

By locating apertures 57 and 58 at different points along the channel it has been found that a variety of diiferent response characteristics other than that shown in FIGURE 6 are achievable. Moreover, if two soundtransducing apparatus are used in a hearing aid, for example, one being used as a microphone and the other as a receiver, it may be desirable to adjust the response curves so that they complement each other. In other words, the peaks of the curve of one transducer may be made to fall in the valleys of the curve for the other.

As is well known, the relatively sudden rise in all three response curves 40, 55 and 60, which lies below 1,000 cycles, is attributable to the effect of Thuras tube 38.

By way of summary, the novel sound-transducing apparatus of the embodiment of FIGURES 14, for example, comprises a sound-transducing device including an electro-mechanical converting assembly to which is connected a diaphragm. Diaphragm 10 and all of the elements mounted therebelow, as shown in FIGURES 2 and 3, collectively constitute such a sound-transducing device. First cover plate 42 is mounted on the sound-transducing device covering, but spaced apart from, diaphragm 10 on the side opposite from the electro-me chanical converting assembly to form a chamber 43 between cover plate 42 and the diaphragm. Second cover plate 47 covers first plate 42. Plates 42 and 47 are formed to provide a channel 50 therebetween extending around at least a portion of the periphery of diaphragm 10 with each of the cover plates having at least one aperture therein (aperture 52 in plate 47 and 53 in plate 42) opening into channel 50 to provide a sound path connecting with the chamber and extending through both plates 42 and 47 and through at least a portion of channel 50.

While particular embodiments of the invention have been shown and described, modifications may be made, and it is intended in the appended claims to cover all such modifications as may fall Within the true spirit and scope of the invention.

We claim: 7

l. Sound-transducing apparatus comprising: a soundtransducing device including an electro-mechanical eonverting assembly to which is connected a diaphragm; a first cover plate mounted on said sound-transducing device covering, but spaced apart from, said diaphragm on the side opposite from said electro-mechanical converting assembly to form a chamber between said first cover plate and diaphragm; and a second cover plate covering said first plate, said first and second plates being formed to provide a channel therebetween with each of said cover plates having at least one aperture therein opening into said channel to provide a sound path connecting with said chamber and extending through both of said plates and through at least a portion of said channel.

2. Sound-transducing apparatus comprising: a soundtransducing device including an electro-mechanical converting assembly to which is connected a diaphragm; a first cover plate mounted on said sound-transducing device covering, but spaced apart from, said diaphragm on the side opposite from said *electro-mechanical converting assembly to form a chamber between said first cover plate and diaphragm; and a second cover plate covering said first plate, said first and second plates being formed to provide a channel therebetween extending around at least a portion of the periphery of said diaphragm with each of said cover plates having at least one aperture therein opening into said chanel to provide a sound path connecting with said chamber and extending through both of said plates and through at least a portion of said channel. p

3. Sound-transducing apparatus comprising: a soundtransducing device including a magnetic'motor assembly to which is connected a diaphragm; a first cover plate mounted on said sound-transducing device covering, but spaced apart from, said diaphragm on the side opposite from said magnetic motor assembly to form a chamber between said first cover plate and said diaphragm; and a second cover plate covering said first plate, said first and second plates being formed to, provide a channel therebetween extending around at least aportion'of the periphery of said diaphragm with each of said cover plates having at least one aperture therein opening into said channel to provide a restricted sound path connecting with said chamber and extending through'in succession one of said plates, at least a portion of said channel, and the other one of said plates.

4. Sound-transducing apparatus comprising: a soundtransducing device including an electro-mechanical converting assembly mounted within, and substantially enclosed on all but one side by, a housing and also including a diaphragm connected to, and substantially covering, said electro-mechanical converting assembly on said one side; a first cover plate mounted'on said soundtransducing device and affixed to said housing covering, but spaced apart from, said diaphragm on the side opposite from said electro-mechanical converting assembly to form a chamber between said first cover plate anddiaphragm; and a second cover plate covering said first plate, said first and second plates being formed to provide a channel therebetween extending around at least a portion of the periphery of said diaphragm with each of said cover plates having at least one aperture therein opening into said channel to provide a sound path connecting with said chamber and extending through both of said plates and through at least a portion of said channel.

5. Sound-transducing apparatus comprising: a soundtransducing device including an electro-mechanica-l converting assembly to'which i connected a diaphragm; a

first cover plate mounted on said sound-transducing device covering, but spaced apart from, said diaphragm on the side opposite from said electron1echanical converting assembly to form a chamber between said first cover plate and diaphragm and having at least a portion of its periphery step-shaped to provide an otfset; and a second cover plate covering said first plate and formed to provide a channel along said ofiset, each of said cover plates having at least one aperture therein opening into said channel to provide a sound path connecting with said chamber and extending through both of said plates. and through at least a portion of said channel. I

6. Sound-transducing apparatu comprising: a soundtransducing device including an electro-mechanical converting assembly to which is connected a generally flat, rectangular shaped diaphragm; a first rectangular shaped cover plate mounted on said sound-transducing device covering, but spaced apart from, said diaphragm on the side opposite from said electro-mechanical converting assembly to form a chamber between said first cover plate and, diaphragm and having at least a portion of its periphery step-shaped to provide an ofiset; and a second rectangular shaped cover plate covering said first plate and formed to provide a channel of substantially square cross-section along said ofiset, each of said cover plates having at least one aperture therein opening into said channel to provide a sound path connecting with said chamber and extending through both of said plates and through at least a portion of said channel.

7. Sound-transducing apparatus comprising: a soundtransducing device including an electro-rnechanical converting assembly to which is connected a diaphragm; a first cover plate mounted on said sound-transducing device covering, but spaced apart from, said diaphragm on the side opposite fromsaid electro-mec'hanical converting assembly to form a chamber between said first cover plate and diaphragm and having three substantially 90 bends around its periphery to provide an offset; and a second cover plate covering said first plate and having only a single 90 bend around its periphery to provide a channel along said offset, each of said cover plates having at least one aperture therein opening into said channel to provide a sound path connecting with said chamber and extending through both of said plates and through at least a portion of said channel.

8. Sound-transducing apparatus comprising: a soundtransducing device including an electro-mechanical converting assembly to which is connected a diaphragm; a first cover plate mounted on said sound-transducing device covering, but spaced apart from, said diaphragm on the side opposite from said electro-mechanical converting assembly to form a chamber between said first cover plate and diaphragm; and a second cover plate covering said first plate, said first and second plates being formed to provide a channel therebetween of a predetermined total length and cross-sectional area extending around and encompassing the entire periphery of said diaphragm with said first cover plate having an aperture therein opening into said channel at one point and said second cover plate having an aperture therein opening into said channel at a diametrically opposite point to provide two sound paths of substantially equal length connecting with said chamber and each extending through both of said plates and through approximately one-half the total length of said channel.

9. Sound-transducing apparatus comprising: a soundtransducing device including an electro-mechanical converting assembly to which is connected a diaphragm; a first cover plate mounted on said sound-transducing device covering, but spaced apart from, said diaphragm on the side opposite from said electro-mechanical converting assembly to form a chamber between said first cover plate and diaphragm; and a second cover plate covering said first plate, said first and second plates being formed to provide a channel therebetween extending around and encompassing the entire periphery of said diaphragm with said first cover plate having two apertures therein opening into said channel at difierent points and said second cover plate having one aperture therein opening into said channel at a point between the points at which the apertures in said first plates are located to provide two sound paths of different lengths connecting with said chamber and each extending through both of said plate and through at least a portion of said channel.

10'. A microphone comprising: a sound-converting device for converting sound waves into electrical signals and including an electro-rnechanical converting assembly to which is connected a diaphragm; a first cover plate mounted on said sound-converting device covering, but spaced apart from, said diaphragm on the side opposite from said electro-magnetic converting assembly to form a chamber between said first cover plate and diaphragm; and a second cover plate covering said first plate, said first and second plates being formed to provide a channel therebetween extending around at least a portion of the periphery of said diaphragm with each of said cover plates having at least one aperture therein opening into said channel to provide a sound path to said chamber and extending through in succession said second cover plate, at least a portion of said channel, and said first cover plate.

11. A receiver comprising: asound-reproducing device for converting electrical signals into sound waves and including an electro-mechanical converting assembly to which is connected a diaphragm; a first cover plate mounted on said sound-reproducing device covering, but spaced apart from, said diaphragm on the side opposite from said electro-mechanical converting assembly to form a chamber between said first cover plate and diaphragm; and a second cover plate covering said first plate, said first and second plates being formed to provide a channel therebetween extending around at least a portion of the periphery of said diaphragm with each of said cover plates having at least one aperture therein opening into said channel to provide a sound path from said chamber and extending through in succession said first cover plate, at least a portion of said channel, and said second cover plate.

12. Sound-transducing apparatus comprising: an electro-mechanical converting assembly; first and second members collectively constituting a cover; and a third member constituting a diaphragm, said cover disposed over said converting assembly and having a shape which with said assembly defines a cavity, said diaphragm disposed beneath said cover in a position which separates said cavity into two chambers, said first and second members laminated together and having a shape which defines therebetween a channel, each of said first and second members having at least one aperture therein opening into said channel and spaced apart to establish a sound path which opens into one of said chambers with said sound path extending through both of said first and second members and through at least a portion of said channel.

References Cited in the file of this patent UNITED STATES PATENTS 2,966,558 Knowles Dec. 27, 1960 

